The present invention relates to a wireless base station, and in particular, relates to a wireless base station which autonomously performs transmission electric power control.
In a wireless communication system, transmission power of radio waves (transmission waves) transmitted from each wireless base station, is influenced by an area (size) of a wireless area (cell) established by the wireless base station. On the other hand, transmission waves from a certain wireless base station, can be interference waves against transmission waves transmitted from another wireless base station, in a cell established by the another wireless base station. For this reason, transmission power of a transmission wave transmitted from each wireless base station needs to be determined by fully considering balance with transmission power of transmission waves transmitted from other wireless base stations present around the wireless base station. In the past, an administrator of a wireless communication system determines transmission power of a transmission wave of a new wireless base station by considering the surrounding radio wave condition and the like, when a new wireless base station is set. However, such human work requires great labor. For this reason, a method for appropriately and effectively determining transmission power of a transmission wave of a wireless base station, has been required. Related techniques for solving the above problem, have been disclosed as follows.
Japanese Patent Application Publication JP-P2004-242076A discloses a wireless access point which can appropriately set transmission power for determining an own radiowave reach area, in relation to adjacent wireless access points. A wireless access point according to Japanese Patent Application Publication JP-P2004-242076A is a wireless access point set in any position to build a wireless network. The wireless access point according to Japanese Patent Application Publication JP-P2004-242076A has a first means and a second means. The first means transmits a test radio wave with initial power which is preliminarily determined as transmission power for determining a radiowave reach area, and judges whether a response signal is received or not from other adjacent wireless access points thereafter, in order to determine initial power based on the judgment result and sets the initial power as own transmission power. The second means transmits a test radio wave with altered power as a result of change from the initial power based on the judgment result in the first setting means, and judges whether a response signal is received or not from other adjacent wireless access points thereafter, in order to determine altered power based on the judgment result and sets the altered power as own transmission power. According to the wireless access point according to Japanese Patent Application Publication JP-P2004-242076A, it is possible to effectively position a small number of access points since own transmission power can appropriately be set in relation to other adjacent access points.
Japanese Patent Application Publication JP-P2006-101442A discloses a variable-cell mobile communication system which can avoid a situation where change in cell size frequently occurs, and which can cope with a cessation of operation of a wireless base station. The mobile communication system according to Japanese Patent Application Publication JP-P2006-101442A, is a mobile communication system for providing wireless communication service by using a plurality of cells of which sizes can be changed into multiple levels. The mobile communication system according to Japanese Patent Application Publication JP-P2006-101442A, has a means to measure a traffic volume in each cell, and a means to store a first threshold value and a second threshold value. The first threshold value is provided as an upper limit of a traffic volume in order to judge whether a cell size should be changed or not, to a cell size which is smaller by one level. The second threshold value, which is smaller than the first threshold value, is provided as a lower limit of a traffic volume in order to judge whether or not the cell size which is smaller by one level, should be changed back into the original cell size. The mobile communication system according to Japanese Patent Application Publication JP-P2006-101442A, is characterized in that a cell size of each cell is automatically changed in accordance with a traffic volume which is successively measured, by using the above means. According to the mobile communication system of Japanese Patent Application Publication JP-P2006-101442A, it is possible to make the mobile communication system operate stably without being unstable around a specific threshold value, and avoid a situation in which handover frequently occurs.
Japanese Patent Application Publication JP-A-Heisei 5-284088 discloses a transmission power controlling method which controls transmission power in accordance with a ever-changing transmission loss situation of an own station, and covers a cell of the own station with a necessary reception level. The transmission power controlling method according to Japanese Patent Application Publication JP-A-Heisei 5-284088, is used in a mobile communication method using cells where a coverage area includes a plurality of cells, a base station is positioned in correspondence to each cell, and a mobile station communicates with one of a plurality of base stations. When a base station transmits a radio wave for judging transmission power, abase station adjacent to the base station detects a reception level of the radio wave for judging transmission power. A control base station, which controls abase station and an adjacent base station, notifies the base station of the reception level detected by the adjacent base station. The base station determines a telegraph power value of the own station based on the notified reception level. According to the transmission power controlling method of Japanese Patent Application Publication JP-A-Heisei 5-284088, it is possible to secure a reception level in a cell of the own station even when a reception level in the cell of the own station changes from moment to moment.
A wireless access point according to Japanese Patent Application Publication JP-P2004-242076A, simultaneously transmits a pilot signal to a plurality of neighboring base stations, and determines transmission power based on a response from each of the neighboring base stations. In an actual wireless communication system however, such processing is not so likely to be applicable since a frequency and a spread code (in the case of a CDMA method: Code Division Multiple Access) used for each base station, are different. In addition, organizing cells with such processing causes interference since cells overlap considerably. While a frequency needs to be changed in order to avoid interference, effective determination of a frequency needs to have a server for controlling transmission power and frequencies. The mobile communication system according to Japanese Patent Application Publication JP-P2006-101442A changes transmission power based on a traffic volume of a wireless base station. For this reason, the mobile communication system according to Japanese Patent Application Publication JP-P2006-101442A needs to have a base station controlling device for collecting a traffic volume and transmitting a control command based on the traffic volume, for transmission power control of a wireless base station. The transmission power controlling method according to Japanese Patent Application Publication JP-A-Heisei 5-284088 needs to have a control base station which receives a transmission wave from a wireless base station and measures a reception level, to notify the wireless base station of the reception level, for transmission power control of a wireless base station.